The invention relates to a vibration damper for vehicles.
Vibration dampers of this type are known (German Offenlegungsschrift No. 1,505,608; FIG. 1).
The regulating member assocated with the valve element of one piston damping valve is provided as an adjusting piston constructed as a stepped piston, which is guided by its circumferential part exhibiting the greater external diameter in a guide cylinder mounted on the piston rod of the vibration damper piston. Further, the regulating member abuts by its other circumferential part or piston part protruding out of the guide cylinder, against the spring washer of the valve element which exhibits the smallest diameter.
By means of the adjusting piston an auxiliary bracing force corresponding to the instantaneous load to be braced is transmitted to the damping valve, which is operative in the traction phase in this vibration damper. This causes the resilience of the spring washers to be correspondingly reduced and thereby increase the flow resistance of this damping valve by a corresponding amount.
This bracing force is generated as a function of the load. One cylinder chamber of the guide cylinder is connected through a connecting channel to another cylinder chamber which is connected to a pressure accumulator of the damper cylinder, and the adjusting piston is thereby stressed by a liquid pressure which is a function of the load.
One object of the invention is to disclose a vibration damper in which the flow resistance of the damping valve, which can be influenced by means of a regulating member, can be varied within wide limits arbitrarily, and thus independent from the pressure prevailing instantaneously in the cylinder chamber in which the valve element is present. This variation is provided to enable the damping to be adapted optimally to driving conditions.
This object is achieved by providing a vibration damper having a cylinder containing a flowable medium. A piston is slidably disposed in this cylinder and creates a first chamber and a second chamber in the cylinder. A piston rod is attached to the piston. A valve member comprising a flowable medium channel in the piston and a valve closure means is also provided. The channel opens into each chamber of the cylinder and the valve closure means covers at least one opening of the channel. The valve closure means exerts a force against the channel. An elastic regulating means is provided for regulating the valve closure force against the channel with a variable force independent of pressure conditions prevailing in the cylinder.
The invention therefore makes possible a planned variation of the valve closure pressure to be generated by the valve closure element, and therefore a desired variation of the characteristic of the vibration damper.
A desired higher damping force pattern of the damper curve is obtained by the operative association of the valve closure element and the regulating member. When the force is increased, the regulating member is progressively applied under pressure to spring washers of the valve closure element in a circumferential direction, and thereby correspondingly varies the resilience of the spring washers and/or hardens the valve closure element accordingly.
The arbitrary influence upon the flow resistance of the relevant damping valve may be exerted by steps or infinitely. It can moreover be realized for all known types of vibration dampers for vehicles, including single-tube and two-tube shock dampers and dampers having a hydro-pneumatic spring on one or on both the damping valves providing in the piston.
The actuating device of the regulating member may operate mechanically or with actuation by pressurized medium.
The variation of the contact pressure may occur automatically as a function of one or more control quantities, particularly dynamic driving quantities determined from the instantaneous driving conditions. While various parameters, such as driving speed, transverse acceleration, longitudinal acceleration, state of load, yawing angular velocity etc., for example, may participate individually or in combination as the determining control quantity.
The variation of the contact pressure may likewise be caused by the driver himself in order to permit a sports driving performance by hardening the shock dampers, for example.
The regulating member may, for example, be constructed in the manner of a cupped spring which may cooperate with a piston. In this arrangement, the cupped spring is braced against the piston on its concave side in its circumferential region.
In a preferred embodiment, the regulating member has a rubber elastic part which is formed as a hollow element. The interior space of this element is connectable to a pressure source. In another embodiment a piston rod can be provided with a feed channel to supply the pressurized medium. The rubber elastic part can be disposed on a bracing element which is slidably disposed on the piston rod and which is retained on a press piston. The press piston, bracing element and rubber elastic part are guided in a cylinder space. The pressurized medium is provided through the feed channel into this cylinder space.
The rubber elastic constitution of the regulating member ensures a stressing of the valve closure element surface area, which is a substantial advantage particularly when the valve closure element is formed by a plurality of spring washers arranged mutually coaxially and exhibiting different external diameters. The rubber elastic material also permits a lightweight construction of the regulating member. Further, the rubber elastic material reacts very rapidly with diminishing contact pressure due to its self-resilience as it returns to its original configuration in a short period of time. A sensitive reaction of the valve closure element is achieved by this means.
Advantageous embodiments are possible for stressing the valve closure element by the regulating member, and favorable structural measures for the arbitrary variation of the valve closure pressure at one or at both damping valves of the piston of a vibration damper as discussed in the description of the invention.